Getter assembly for electron tubes



Nov. 30, 1965 J. J. FREE ETAL 3,

GETTER ASSEMBLY FOR ELECTRON TUBES Filed Nov. 19. 1962 EAR/0M 2041(MI/MUM) 4 6f 67 INVENTORS JOHN W- GAYLORD, AND JEROME J. FREE UnitedStates Patent 3,221,201 GETTER ASSEMBLY FOR ELECTRON TUBES Jerome JosephFree and John W. Gaylord, Lancaster, Pa.,

assignors to Radio Corporation of America, a corporation of DelawareFiled Nov. 19, 1962, Ser. No. 238,680 6 Claims. (Cl. 313177) The presentinvention relates to improved getter assemblies of the type in which aflashable getter is raised to flashing temperature by the passage ofelectrical current therethrough.

The invention finds particular utility in electron tubes havingceramic-metal parts. The manufacture of tubes of this type usuallyinvolves loosely assembling on a jig ceramic and metal parts with theceramic parts suitably metalized and baking the parts so assembled in anoven having suitable temperature and atmosphere ambient for mutuallyfixing the parts. Oven baking for fixing the parts has been founddesirable because the fixed junctures between the parts formed by theoven heating are characterized by greater freedom from strains than ifperformed by techniques involving localized heating of the parts.

The parts involved in the assembly and baking operations referred to,include electrode sub-assemblies and envelope parts. The envelope partsemployed form an enclosure that is complete except for an exhaustopening and an opening through which a cathode sub-assembly later may beextended and sealedacross by localized heat.

It is found that after the envelope has been initially evacuated throughthe exhaust opening to a desirably low gas pressure, and the exhaustopening sealed, gases oceluded in the metal and ceramic parts within theenvelope are released to an extent that is objectionable in certainapplications. While this problem is solved in other tube types by meansof getters that chemically combine with the released gases, the use .ofgetters in tubes of the type under consideration has not been fullysatisfactory.

One type of getter that is highly efficient to take up gases releasedafter evacuation of a tube comprises barium suitably sheathed forprotection from the atmosphere. The sheath is made of electricallyconductive material, such as nickel or aluminum, and may be providedwith a relatively thin portion constituting a zone of Weakness. When thesheath is heated, the barium therein provides a pressure sufficientlyhigh to rupture the sheath at its zone of weakness, and to liberatebarium in the form of a flash.

Difiiculty has been experienced in using this type of highly eficientgetter in ceramic metal tubes of the type discussed. Incorporation ofthe getter in the tube structure prior to the oven baking thereof hasnot been found feasible because the temperature employed is high enoughto flash the getter prematurely. Subsequent introduction of the getterinvolves difficulty because the only available openings in the tubeenvelope after baking are inadequate -for this purpose. For example, theexhaust opening is too small to permit extension of a gettertherethrough and a fixing of a getter within the envelope. Furthermore,the opening for receiving the cathode sub-assembly is not suitable forgetter introduction. If the getter is introduced through the openingprovided for the cathode sub-assembly, prior to extension of thissub-assembly into the envelope, a flashing of the getter will depositgetter material on the adjacent electrodes, which is harmful to theiroperation. If the getter is mounted within the cathode sub-assembly andintroduced into the tube envelope with this sub-assembly, the flash fromthe getter may be shielded from regions of the interiorof the tubeenvelope other than that encompassed by the cathode subassembly. This isparticularly true in tube types employing the cathode-heatersub-assembly described in co-pending application Serial No. 199,404filed June 1, 1962, by F. R. Ragland, Jr., and assigned to the sameassignee as the present application.

Moreover, in tube types having ceramic-metal envelopes, it is notreadily feasible to heat the getter to flashing temperature byexteriorly positioned means for inducing electrical currents in thegetter structure nor by directly connecting spaced portions of thegetter structure across a suitable electrical current supply.

Accordingly, it is an object of the present invention to provide animproved electron tube.

It is a further object to provide an electron tube having an improvedgetter assembly.

Another object is to provide an improved getter structure for the use inassociation with an electron tube having an envelope that is subjectedto a brazing operation prior to evacuation, at a temperature higher thanthe temperature at which the getter flashes.

A further object is to provide a getter structure of the type in whichthe getter is heated to flashing temperature by electric current lossestherein, in association with an electron tube having a ceramic-metalenvelope.

Another object is to provide a novel getter-exhausttubulation assemblywherein the exhaust tubulation is spaced from the tube envelope andconstitutes an electrical lead to a getter structure.

A further object is to provide an electron tube in which a getterstructure is electrically connected across an anode and an exhausttubulation of the tube for flashing by establishing a suitable potentialdiiference between the anode and the exhaust tubulation.

In one example of the invention, an electron tube having a ceramic-metalenvelope, is provided with an exhaust opening in one end of theenvelope. A chamber having walls fixed to the envelope end referred to,and provided with an opening communicating with the exhaust opening,supports an exhaust tubulation in spaced coaxial relation with respectto the exhaust opening. The chamber walls include an insulating memberelectrically isolating a portion thereof including the exhausttubulation, from other wall portions including those in engagement withthe tube envelope. In the example discussed, the tube envelopeportionengaging the aforementioned chamber, comprises an external anode.An elongated getterstructure has one end fixed to the aforementionedwall portions engaging the anode, and the other end fixed to the wallportion that includes the exhaust tubulation. The getter structureincludes a metal sheath made of a aluminum or nickel and having arelatively thin zone of weakness therein. Within the sheath is disposeda body or slug of substantially pure barium intermixed with particles ofaluminum. When the exhaust tubulation and anode are connected across asuitable electrical power suuply the sheath and barium will becomeheated by electrical losses therein to a temperature sufficiently highto cause the barium to develop .a pressure within the sheath of suchmagnitude as to rupture the zone of weakness in the sheath and to resultin a flash of barium vapor. The portion of sheath having the zoneWeakness is oriented in the chamber in such a way as to direct thebarium flash to a region where its electrically conductive characterwill result in least harm. The resultant barium coating deposited inthis region will serve as a continuing take-up agent for gases liberatedwithin the tube. This function is facilitated because of thedisplacement of the exhaust tube from the exhaust opening in the anode.

Further features and objects of the invention will become evident as the:present description continues.

In the drawing:

FIG. 1 is an elevation, partly in section, of an electron tube andgetter assembly incorporating the invention;

FIG. 2 is an exploded elevational view in section showing the sequencein which the parts constituting the structure shown in FIG. 1, areassembled;

FIG. 3 is a longitudinal sectional view of a getter structure employedin the tube shown in FIG. 1; and

FIG. 4 is a sectional view taken along the line 44 of FIG. 3, and showsthe zone of weakness in the sheath of the getter structure depicted inFIG. 3.

The electron tube structure shown in FIG. 1 comprises an electron tubehaving a getter and exhaust tube assem bly 12. The electron tube 10 maybe of the tetrode type described in co-pending application Serial No.182,908 filed March 27, 1962, by J. W. Gaylord, and assigned to the sameassignee as the present application. The tube 10 includes a heater 14, acathode 16, a control grid 18, a screen grid 20, and an external anode22. These electrodes, with the exception of the heater 14, terminate indownwardly turned flanges comprising anode flange 24, screen grid flange26, control grid flange 28 and cathode flange 30. These flanges areinsulated from each other as shown in the aforementioned Gaylordapplication, by means of ceramic rings. The upper end of the anode 22has an exhaust opening 32. The tube 10 may be made and assembled inaccordance with the method described in US. Patent 2,980,984 to M. B.Shrader et al. issued April 25, 1961, and assigned to the same assigneeas the present application.

The getter and exhaust tube assembly 12 includes a dish-shaped metallicmember 34 fixed as by brazing to the outer top wall of the anode 22.Member 34 is provided with an opening 36 communicating with the exhaustopening 32. The member 34 is also provided with an outwardly extendingradial flange 38, to which is fixed as by welding, an outwardlyextending radial flange 40 of an inverted dish-shaped metallic member 42having an opening 44 in register with openings 32 and 36. To the innersurface of member 42 is brazed one metallized surface of a ceramic ring46 which is in coaxial relation with opening 44. To the other surface ofthe ceramic ring 46, is brazed a metal eyelet 48 including an outwardlyextending flange 50 engaging the ring, and a tubular portion 52. Thetubular portion 52 has an inner diameter for snugly receiving an exhausttubulation 54 in coaxial relation with openings 32, 36. The exhausttubulation 54 is suitably fixed to the eyelet 48, as by brazing in aposition to provide an appreciable space between the lower end 56 of thetubulation and the dish shaped member 34 This space provides desiredcommunication between interior of the getter chamber defined by thedish-shaped members 34, 42 and the interior of the envelope of tube 10,for a purpose to be described. The exhaust tubulation 54 is pinched offat 58 in a vacuum-type seal.

Within the chamber defined by the dish-shaped members 34, 42 ispositioned an elongated getter structure 60 having one end tab 62 fixedas by spot welding to the inner wall of the upper dish-shaped member 42,and another end tab 64 fixed as by spot welding to the eyelet 48. Itwill be noted that in this arrangement, the elements to which the endtabs of the getter structure are fixed, are in electrically insulatedrelation. Thus by connecting a suitable electrical potential across theexhaust tubulation 54 and the anode 22, electric will follow through thegetter structure 60 for heating it to a flashing temperature.

The getter structure as shown in FIGS. 3 and 4 comprises a sheath 65having a thinned down portion 66 constituting a zone of weakness. Withinthe sheath 65 is disposed at body or slug 67 of substantially purebarium mixed with particles of aluminum. This getter structure is sooriented in the space or chamber defined by the dishs'haped members 34,42 that the flash will occur in a direction where it will be leastharmful to tube operation.

Such orientation may include positioning the getter structure 60 in sucha way that its relatively thin wall portion 66 (FIGS. 3 and 4) extendsdownwardly so that the flash will be directed to the lower left-handcorner portion 68 (FIG. 1) of the aforementioned chamber. In this way,the flash will be directed away from the opening 32 to preventcontamination of the electrodes of tube 10. The Zone of weakness in analternative arrangement, may be positioned to face upwardly. In thisposition most of the getter flash will impinge upon the lower surface offlange 50 of the eyelet 48. Since there is a likelihood that someportion of the flash will coat the edge of ceramic ring 46 and therebyprovide a parallel and more conductive path for electrical energy, thanthat provided by the getter structure 60, and thereby prevent a completeflash of the getter, it is preferred to mount the getter in such amanner that its zone of weakness 66 faces the lower left hand corner 68of the chamber defined by members 34, 42, as viewed in FIG. 1.

The barium deposited in the corner region 68 (FIG. 1) will serve acontinuing gas absorbing function with respect to gases evolved withinthe tube 10. This is rendered feasible because of the spaced mounting ofthe exhaust tubulation 54 from the opening 32, as a consequence of whicha free path is provided between the corner portion 68 and the interiorof tube 10.

In one example, a getter structure comprising a sheath 65 made of nickeland containing about 0.012 gram of a mixture of pure barium and aluminumwas successfully flashed by connecting the anode 22 and exhausttubulation 54 across a potential source of alternating current at avoltage of about 0.7 volt and a current of about 12 amperes, for 8seconds. Suitable connections to the anode and exhaust tubulation wereeffected by means of metal clamps embracing these elements.

In assembling the parts constituting the electron tube shown in FIG. 1care must be taken to avoid a premature flashing of the getter 60. Tothis end, the parts comprising the tube 10 and the dish-shaped member 34are assembled and mutually fixed apart from the sub-assembly 70 (FIG. 2)which includes the getter 60.

The assembling and fixing of the parts of the tube 10 and thedish-shaped member 34 may be effected in accordance with the methoddescribed in the aforementioned Patent Number 2,980,984. Thus thecontrol grid 18 and screen grid 20 may be first mutally fixed inimperforate tubular blank form, with an insulating ring disposed betweenradially extending flanges 26, 28 thereof. Radial openings are then cutin the tubular portions of the blanks by an erosion technique such aselectrical discharge machining. In fixing the two grid blanks to thesuitably metalized insulating rings, a relatively high melting pointsolder should be used, such as commercially available BT solder having aflow point of 780 C. This is because the operation of mutally fixing thetwo grid blanks and the later operation of fixing the anode 22 anddish-shaped number 34 to the grid assembly, are performed in an oven inorder to prevent the development of objectionable strains in the regionsof the joints. This multiple-step fixing operation requires that thebrazing material or solder initially employed, have a higher meltingpoint than the solder employed in subsequent brazing operations.Otherwise, a later brazing operation would result in a loosening anddisplacement of the parts previously jigged and brazed.

To reduce the number of later oven operations involving oven heating andthereby permit the final oven operation to be carried out using a solderthat has a melting point only slightly lower than that of BT solder, thelater operation may involve jigging the grid assembly into coaxialrelation to the anode 22, a cathode fixing flange 30, and suitablymetallized insulating rings disposed between the previously formed gridassembly and the anode, and between the cathode fixing flange 30 and thegrid assembly. The solder used in this final brazing operation may beRTSN solder which is commercially available and has flow pointtemperature of 720 C.

After the parts have been brazed in accordance with the foregoing, asub-assembly comprising the cathode 16 and the heater 14 is telescopedinto the control grid 18. This sub-assembly has a flange which nests inthe cathode flange 30 (FIG. 1) as shown in the aforementioned Patent2,980,984, when the sub-assembly is in coaxial relation with the controlgrid 16. The flange of the cathode heater sub-assemblly is fixed to thecathode flange 30 by means of localized heat, such as heliarc welding.This completes the assembling and fixing of parts comprising the tubeand the dish-shaped member 34.

The parts comprising the sub-assembly 70 (FIG. 2) with the exception ofthe getter 60 are then jigged into coaxial relation. BT solder isinterposed between the two opposite metalized surfaces of ceramic ring46 and the surface portions of the cup-shaped member 42 and eyeletflange 50 engaged by the ring 46. BT solder is also interposed betweenthe exhaust tubulation and the eyelet. While so jigged the assembly isbrazed in an oven at a temperature of 820 C. Thereafter, the tabs 62, 64(FIG. 3) of the getter structure 60 are spot-welded across thecup-shaped member 42 and the eyelet 48. This subsequence in assemblingthe parts of sub-assembly 70 preserves the getter structure 60 fromharmful heat.

The final assembling step comprises jigging assembly 70 into coaxialrelation with respect to the tube 10 and the dish-shaped member 34 fixedthereto (FIG. 1) to dispose the flanges 38, 40 of the two dish-shapedmembers in abutting relation. In this relation the two flanges aremutually fixed by localized heat such as that involved in heliarcwelding.

The envelope of the tube structure formed by the aforementionedassembling and fixing operations is evacuated through exhaust tubulation54 and thereafter the tubulation is sealed in a pressure weld 58 formedwithout the deliberate application of heat.

After the evacuation of the tube envelope, the getter structure isflashed by connecting a suitable power source across the portion of theexhaust tubulation 54 remaining after sealing, and the anode 22, asdescribed in the foregoing.

We claim:

1. An electron tube comprising:

(a) an envelope having electrodes therein, said envelope having anexhaust opening in a wall thereof,

(b) a chamber fixed to an outer surface of said wall and having anopening communicating with said exhaust opening,

(c) an exhaust tubulation supported in said chamber in coaxial relationwith said exhaust opening and having a free end portion extending intosaid chamber,

(d) and a getter structure supported in said chamber.

2. An electron tube comprising:

(a) an envelope having an exhaust opening therein,

(b) a chamber having a metal wall mounted upon an outside surface ofsaid envelope, said chamber having an opening communicating with saidexhaust opening,

(0) metallic means supported in said chamber and insulatingly extendingthrough said wall for mechanically evacuating the interior of saidenvelope and chamber,

((1) and an elgonated getter positioned in said chamber to direct aflash of gettering material away from said exhaust opening, one end ofsaid getter being fixed to said means and the other end being fixed tosaid metal wall.

3. An electron tube having:

(a) a first envelope,

(b) electrodes supported in said first envelope,

(c) a second envelope joined to said first envelope,

(d) said first and second envelopes having registering openings,

(e) said second envelope including two metallic wall portionselectrically insulated from each other,

(f) and a getter in said second envelope connected across said portions,whereby said getter may be flashed by impressing a predetermined voltagedifference on said two portions, said getter comprising a materialincluding barium and aluminum and having a structure for directing theflashed barium to a region within said second envelope remote from saidopenings.

4. An electron tube having:

(a) an envelope having metallic walls,

(b) a partition wall within said envelope forming two chambers, saidwall having an opening providing communication between said chambers,

(c) a plurality of electrodes in one of said chambers,

((1) structure including a metallic exhaust tubulation insulatinglysupported in the other of said chambers, said exhaust tubulation beingspaced from said opening, said other of said chambers having one of saidmetallic Walls,

(e) and an elongated flashable getter structure having one end fixed tosaid exhaust tubulation structure and the other end fixed to said one ofsaid metallic Walls of said other of said chambers electricallyinsulated from said exhaust tubulation structure.

5. An electron tube having:

(a) an envelope forming two compartments having a common wall,

(b) said Wall having a relatively small opening therein,

(0) one of'said compartments being defined by two metal wall portions,

(d) an insulating member interposed between said wall portions,

(e) a flashable getter structure connected across said wall portions,

(f) an exhaust tubulation mounted on one of said wall portions andhaving a free end in closely spaced relation with respect to saidopening, the other of the said wall portions comprising a portion ofsaid wall,

(g) and a plurality of electrodes positioned in the other of saidcompartments.

6. An electron tube having:

(a) an envelope forming two compartments having a common wall,

(b) said wall having a relatively small opening therein,

(c) one of said compartments being defined by two spaced metallic wallportions,

(d) an insulating member interposed between said wall portions,

(e) a flashable getter structure connected across said wall portions,

(f) an exhaust tubulation mounted on one of said wall portions andhaving a free end in closely spaced relation with respect to saidopening and another end extending outside of said envelope,

(g) and a plurality of electrodes positioned in the other of saidcompartments,

(b) said getter structure being positioned to direct a getter flash to aregion remote from said opening, whereby said electrodes are free fromcontamination by flashed getter material.

References Cited by the Examiner UNITED STATES PATENTS GEORGE N. WESTBY,Primary Examiner.

1. AN ELECTRON TUBE COMPRISING: (A) AN ENVELOPE HAVING ELECTRODESTHEREIN, SAID ENVELOPE HAVING AN EXHAUST OPENING IN A WALL THEREOF, (B)A CHAMBER FIXED TO AN OUTER SURFACE OF SAID WALL AND HAVING AN OPENINGCOMMUNICATING WITH SAID EXHAUST OPENING, (C) AN EXHAUST TUBULATIONSUPPORTED IN SAID CHAMBER IN COAXIAL RELATION WITH SAID EXHAUST OPENINGAND HAVING A FREE END PORTION EXTENDING INTO SAID CHAMBER, (D) AND AGETTER STRUCTURE SUPPORTED IN SAID CHAMBER.